1. Field
The present disclosure relates to tires suitable for bearing heavy loads, and to a use of a low hysteresis rubber composition for improving the stiffness of treads of such tires. The disclosure applies to tires for motor vehicles, such as heavy-duty vehicles, civil engineering vehicles or aircraft.
2. Description of Related Art
In the field of the manufacture of tires suitable for bearing heavy loads, especially for heavy-duty vehicles, and in particular in the field of the formulation of rubber compositions in contact with the ground, referred to as treads, use is made, in a known manner, of natural rubber on account of the low hysteresis losses that this elastomer has.
Very particularly for these tires intended to bear heavy loads, it is desirable for the materials constituting the treads to have a good stiffness at low and moderate deformations, while being capable of accepting certain deformations without being damaged under the effect of higher stresses or deformations that are amplified by the loads borne. In other words, it is desirable to have a material based on natural rubber which, while being stiff at low and moderate deformations so as to provide the tire with a low rolling resistance, has a high elongation at break or a high tensile strength so as to provide satisfactory wear resistance. However, these gains in properties must not be attained at the expense of the gain in hysteresis already achieved with the use of natural rubber.
The Applicant companies' patent application WO 2012/007442 describes the modification of a diene elastomer by grafting with a specific modifier comprising at least one nitrogen-containing dipole and at least one nitrogen-containing associative group. The elastomer thus modified endows a composition containing it with improved hysteresis properties, and also a good stiffness under moderate deformation and a high elongation at break.
However, it turns out that this modification applied to natural rubber does not provide the expected properties. Thus, a tire suitable for bearing heavy loads, the tread of which comprises a composition based on natural rubber modified by a modifier comprising at least one nitrogen-containing dipole and at least one nitrogen-containing associative group according to WO 2012/007442 does not exhibit the desired compromise of properties which combines a low rolling resistance and a satisfactory wear resistance in optimal proportions.
Yet for the designers of tires intended to bear heavy loads, improving the compromise of performances of the tires, especially the rolling resistance and the wear resistance, by improving the compromise of often conflicting properties of the compositions constituting the tires, such as a good stiffness at low and moderate deformation and a high elongation at break of the compositions, is a constant concern.